NMR Spin-Spin Coupling Constants Derived from Relativistic Four-Component DFT Theory-Analysis and Visualization.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Nuclear Magnetic Resonance (NMR) indirect spin-spin coupling constants (SSCCs) are crucial for understanding molecular structure and bonding.
• Current SSCC analysis and visualization tools are limited to nonrelativistic quantum chemistry.
• Relativistic effects are known to significantly influence properties involving heavy elements.

Purpose of the Study:

• To develop and implement novel relativistic methods for the visualization of SSCCs.
• To analyze and interpret relativistic effects on SSCCs involving heavy atoms (Se, Te).
• To improve the accuracy of theoretical SSCC calculations by incorporating relativistic effects and conformational analysis.

Main Methods:

• Theoretical development of relativistic SSCC visualization based on SSCC densities and first-order current densities.
• Implementation of these techniques within the ReSpect program package.
• Calculation of SSCCs using nonrelativistic, scalar relativistic, and four-component relativistic density functional theory (DFT).

Main Results:

• Demonstrated relativistic SSCC visualization techniques for heavy-atom couplings (Se-Se, Se-Te, Te-Te).
• Quantified substantial relativistic effects for Se-Se, very significant for Se-Te, and non-negligible for Te-Te couplings.
• Showed that considering a second molecular conformation substantially improves theoretical SSCC values.

Conclusions:

• Relativistic effects are essential for accurate SSCC calculations involving heavy elements.
• The developed relativistic visualization methods provide new insights into coupling pathways.
• Incorporating relativistic theory and conformational flexibility enhances the predictive power of computational chemistry for NMR parameters.